1. Field of the Invention
The present invention relates to an image forming apparatus that is configured to, even if a transport error of a recording sheet occurs, continue transporting a recording sheet without stopping the apparatus and discharge the recording sheet remaining in the apparatus, and is provided with a container unit that holds the discharged recording sheet.
2. Description of the Related Art
Image forming apparatuses are known that include a discharge unit for discharging a recording sheet remaining in the image forming apparatuses when a recording sheet becomes jammed.
Japanese Patent Laid-Open Publication No. 2-257158 (Patent Document 1) discloses an image forming apparatus having a double-sided printing device that performs double-sided printing by reversing and re-feeding recording sheets. This image forming apparatus includes a discharge unit that discharges a recording sheet remaining in the image forming apparatus body upon occurrence of a jam.
Japanese Patent Laid-Open Publication No. 2002-268304 (Patent Document 2) discloses a copying machine that identifies a recording sheet having both sides printed and remaining in the apparatus body upon occurrence of a jam and, if the identified recording sheet is not the jammed sheet, discharges the identified, recording sheet. More specifically, the copying machine of Patent Document 1 performs double-sided printing while circulating plural recording sheets in a transport path. If a paper jam occurs in the transport path, the copying machine determines whether to discharge a recording sheet based on recording sheet discharge destination information (information indicating whether a recording sheet is to be discharged out of the machine body or to be transported to a reverse path) and position information indicating the position of the recording sheet in the transport path. If the recording sheet is determined to be discharged and if the recording sheet is determined not to be a jammed sheet based on paper jam information of the recording sheet, the copying machine discharges the recording sheet. This prevents the effective (printed) recording sheet from being wasted.
Japanese Patent Laid-Open Publication No. 56-8163 (Patent Document 3) discloses a recorder that detects the status of a recording sheet in a transport path such as warping and skewing and, if the status is not allowable, guides the recording sheet in a direction different from the feeding direction to remove the recording sheet from the transport path, thereby preventing a jam.
A detailed description of the image forming apparatus of Patent Document 1 is given below.
FIG. 15 illustrates the image forming apparatus (laser printer) of Patent Document 1. This apparatus includes, as integral parts, an image forming apparatus body 1 and a double-sided printing device 2. Referring to FIG. 15, image formation is performed using a usual electrophotographic process. More specifically, a recording sheet fed from a feed tray 1A, 1B, or 1C is transported to a photoreceptor 4 by feed rollers 2A, 2B, or 2C and registration rollers 3. Then processes such as charging, exposure, development, transfer, and fixing are performed by a charger 5, an optical unit 6, a developing unit 7, and a transfer charger 8, a fixing unit 9, etc., so that an image is formed. The recording sheet with one side printed is discharged from the fixing unit 9 to a discharge tray 10 or the double-sided printing device 2. Whether to discharge the recording sheet to the discharge tray 10 or to the double-sided printing device 2 is selected according to switching control of discharge rollers 11 and a switching claw 12. For discharging the recording sheets to the double-sided printing device 2, the recording sheets are transported to a transport path including reverse rollers 13 by controlling the switching claw 12. Then the recording sheets are switched back one by one to a sheet transport path b by controlling the reverse rollers 13 and the reverse claw 14. The recording sheet with one side printed is thus reversed and transported by feed rollers 15 to the registration rollers 3 to have the other side printed. It is to be noted that the units performing the image forming process are driven by a main motor 16.
Referring to FIG. 16, in this image forming apparatus, a transport direction switching unit (switching claw 18) is disposed over a recording sheet inlet 17. The switching claw 18 switches the transport direction between the discharge direction and the direction of a reverse transport path toward the double-sided printing device 2. If a jam occurs in the double-sided printing device 2, a recording sheet remaining in the image forming apparatus body 1 is discharged into a container basket 20 via an opening 19.
In this image forming apparatus, in the case of printing a large number of sheets at a time, recording sheets are sequentially fed from the large capacity feed tray 1C, and plural (three or four) recording sheets are transported simultaneously in the entire transport path, for example. In this case, the first, second, and third recording sheets are sequentially fed from the feed tray 1C into the image forming apparatus body 1 to form images on the front sides of the recording sheets. After the front side of the third sheet is printed, the first recording sheet is re-fed from the double-sided printing device 2 to have its back side printed. Then, the fourth recording sheet is newly fed to have its front side printed. That is, in this case, printing is performed on the front side of the first recording sheet, the front side of the second recording sheet, the front side of the third recording sheet, the back side of the first recording sheet, the front side of the fourth recording sheet, the back side of the second recording sheet, . . . , in this order. In this manner, printing is performed alternately on the front side of a recording sheet and the back side of another recording sheet.
Assume that, in the above described case, when the back side of the first recording sheet is printed but the front side of the fourth recording sheet is not yet printed, the third recording sheet with the front side printed becomes jammed in the transport path b. In such a case, the main motor 16 is stopped. Then, the transport system of the image forming apparatus body 1 is driven to discharge the unprinted fourth recording sheet remaining in the image forming apparatus body 1 (for example, remaining in front of the fixing unit 9 at the time of occurrence of the jam) into the inlet 17. Then the main motor 16 is restarted to print the back side of the second recording sheet (for example, the recording sheet remaining in front of the photoreceptor 4 at the time of occurrence of the jam) having the front side already printed.
As described above, in the image forming apparatus of Patent Document 1, if a recording sheet becomes jammed in the transport path b in the double-sided printing device 2, an unprinted recording sheet in the image forming apparatus is discharged. A recording sheet with the front side printed is transported to a position where printing is performed to have its back side printed. That is, if a jam occurs, a recording sheet with one side printed proceeds to have the other side printed, while the unprinted recording sheet is discharged for reuse. Only the jammed recording sheet needs to be removed by a user, and therefore the recovery process can be performed quickly.
However, none of the above Patent Documents teaches of suggests a technique for continuing transporting recording sheets, including a recording sheet causing a transport error, remaining in the apparatus to discharge the recording sheets out of the apparatus.
More specifically, Patent Document 1 aims to prevent a recording sheet from being wasted when a jam occurs in the apparatus. For this aim, the image forming apparatus of Patent Document 1 discharges a recording sheet circulating in the apparatus without performing any further printing operation or discharges after printing the back side depending on the printed state of the recording sheet. However, the image forming apparatus does not transport the jammed sheet or a recording sheet whose path is blocked by the jammed sheet.
Similarly, Patent Document 2 aims to prevent an effective (successfully recorded) recording sheet from being wasted, and only discusses how to discharge the effective recording sheet that is not jammed upon occurrence of a jam.
Patent Document 3 aims to prevent a recording sheet from being jammed in a transport path and only discusses quick removal of a warped or a skewed recording sheet from the transport path.
Meanwhile, users who print a large number of sheets at a speed of, e.g., about 90 sheets per minute demand not only a high printing speed but also reducing the time required to perform a recovery process from a transport error of a recording sheet.